A Synthesis of the Carbon Skeleton of Maoecrystal V

Abstract

An enantioselective synthesis of the maoecrystal V (1) carbon skeleton is described. The key transformations include arylation of a 1,3-dicarbonyl compound with a triarylbismuth(V)dichloride species, oxidative dearomatization of a phenol, and a subsequent intramolecular Diels-Alder reaction.Maoecrystal V (1, Figure 1) was isolated and characterized in 2004 by Sun and coworkers from the Chinese medicinal herb Isodon Eriocalyx. 1 It possesses an unusual architecture rendering it the most modified naturally occurring ent-kauranoid isolated to date. 2 The structure was confirmed by X-ray crystallographic analysis to contain five highly congested rings and seven stereocenters, two of which are adjacent all carbon quaternary centers located in its interior. One of these all carbon quaternary centers is also the bridgehead carbon of the [2,2,2]-bicyclooctanone moiety. This letter reports an early approach to 1 pursued in our laboratory from

Dearomatization Strategies in the Synthesis of Complex Natural Products

“…The highly reactive, dearom- In an early approach to maoecrystal V (48), Baran and coworkers also executed an ortho-oxidative dearomatization/ IMDA sequence to create the core of the natural product (Scheme 26). [65] Treatment of the advanced aryl ketone 185 with TFA simultaneously removed the ether protecting group and induced cyclization to afford hemiketal 186 in 65 % yield.…”

“…Approach to maeocrystal V using oxidative ortho-dearomatization/IMDA cycloaddition ). [65] biomimetic pathway towards several neolignan natural products, but also the careful handling required to access the highly oxygenated and sensitive intermediates.…”

Desaromatisierungsstrategien in der Synthese strukturell komplexer Naturstoffe

“…In ersten Studien zur Synthese von Maoecrystal V ( 48 ) verwendeten Baran et al. ebenfalls eine Sequenz aus ortho ‐oxidativer Desaromatisierung und IMDA‐Cycloaddition zum Aufbau der Kernstruktur des Naturstoffs (Schema ) 65. Die Umsetzung des hoch substituierten Arylketons 185 mit TFA entfernte die Etherschutzgruppe und induzierte gleichzeitig die Cyclisierung zum Halbketal 186 (65 % Ausbeute).…”

“… Zugang zu Maeocrystal V durch oxidative ortho ‐Desaromatisierung/IMDA‐Cycloaddition (Baran et al., 2009) 65…”

The Synthesis and Antimicrobial Activity of Heterocyclic Derivatives of Totarol

“…A formate group was installed by a Claisen condensation as a means to synthesize heterocyclic derivatives on the A-ring of (+)- 2 (Scheme 1). 16 Treating (+)- 2 with sodium hydride, methanol, and ethyl formate produced intermediate (+)- 5 in 73% yield. Azoles (+)- 6 and (+)- 7 were prepared as their methyl ethers (not shown) by treatment of (+)- 5 with hydrazine monohydrate or phenylhydrazine hydrochloride, respectively.…”